1. Field of the Invention
The invention relates to a container for storage of refrigerated liquids, in particular for liquefied gases, which comprises a reinforced concrete or prestressed concrete outer container and a steel inner container placed into the outside container.
2. Brief Description of the Background of the Invention Including Prior Art
The use of gas as an energy carrier in private and industrial spheres has increased in recent times. In addition to the transport of the gas from remote production places to the user, the gas is also transported by ship after liquefaction. The liquefied gas then also requires corresponding stationary storage provisions, where the prescribed safety provisions have to be met.
The formation of an inner and outer container depends on what kind of safety provisions have to be met in order to prevent in extraordinary cases transmission of effects from the outside to the inside or in case of a leak to prevent the exit of gas from the inside to the outside.
Frequently, an open steel inner container disposed in a steel reinforced concrete or prestressed concrete container closed at all sides is required for the storage of liquefied natural gas (LNG). Liquid ammonia, butane, and ethane are frequently stored in closed steel containers, which are positioned in steel reinforced concrete or prestressed concrete containers open at the top.
The insulation depends on the kind of the gas. In case of the storage of liquefied natural gas, which has to be stored at a temperature of about -160 degrees centigrade, the interspace is completely filled with insulating material. Since the intermediate space not only serves for the placement of insulation, but also has to be present in case of disturbances or required repair works, usually expanded Perlite is employed as insulating material. The starting material for the expanded perlite is volcanic silicate containing rock, where upon short term heating to about 1000 degrees centigrade the bound water is transformed into vapor such that the glass melt is popped to a multiple of its original volume. If required, the perlite can be removed from the interspace.
If liquefied butane gas is to be stored in the container then a complete filling of the interspace with insulating material is not required, since the storage temperature for liquid butane gas is only at about -10 degrees centigrade and therefor a thin insulating layer, for example from polyurethane, on the outer circumference of the inner container is sufficient.
Substantial safety provisions have to be arranged in order to operate such a container. On the one hand, the outer container has to be stable against earthquakes, but on the other hand also the loads arising from a cloud of gas explosion have to be supported. Also, the load case where the inner container suddenly rips open has to be provided for. Since steel tends to be brittle at low temperatures, defects in the steel material can in fact, result in the situation where an initially small breakage area expands to a continuous fracture. The result is that the refrigerated liquid pours out of the crack and pours into the intermediate space between the steel inner container and the steel reinforced concrete outer container and flows from the exit location in two directions into the intermediate space.
Considering initially the simplified case where no insulating material is disposed in the interspace, then the flow of liquid runs into two directions within the interspace until the two partial streams meet at the side approximately diametrical to the breakage point. Model experiments have demostrated that then at this position a pressure is exerted onto the steel reinforced concrete, which locally reaches up to the sixfold hydrostatic pressure such that thereby the steel reinforced concrete containers are impermissibly loaded.
Such a liquid flow can also then occur if the intermediate space between the inner and the outer container is filled with sufficiently permeable and/or displaceable material such as for example expanded perlite.
At any rate, a bursting or rupturing of the steel inner container would result in case of the known containers in having the liquid gas pour in a gush into the intermediate space and either displace the light weight perlite material or run along the free space of the annular slot, such that the encounter of the pouring out liquid gas at the side disposed diametrically opposite results in an impermissible loading of the steel reinforced concrete outer container.